For driving loads, drive modules are known which are connected in series with the load between terminals for supply potentials which serve for applying a supply voltage to the load according to the control signal. In this case, so-called high-side modules are connected between a terminal for positive supply potential and the load, whilst so-called low-side modules are connected between the load and a terminal for negative supply potential or reference potential. That connection of the load which is remote from the drive module is connected to the respective further supply potential terminal.
One example of a drive module formed as a high-side module is the integrated component BTS441T from Infineon Technologies AG, Munich which is described in the data sheet BTS441T, Oct. 1, 2003. This drive module has a power transistor, the load path of which in the module is connected between a first connection for connecting the load and a second connection for applying a supply potential. During the operation of the module, the transistor is driven in the on state or in the off state by means of a driver circuit according to a drive signal present at a control input, in order to drive the load according to said drive signal. In the case of such a module, which is also referred to as a smart high side power switch, the driver circuit also comprises a protection circuit for protecting the transistor against overtemperature. Furthermore, the driver circuit may also have a measuring arrangement for measuring a current flowing to the load and an arrangement for limiting said current. In this regard, reference is made to the data sheet of the integrated component BTS5434G, V1.0, Jan. 23, 2004, Infineon Technologies AG, Munich. The current measuring arrangement may function according to the so-called current sense principle, for example, which is described in DE 195 20 735 A1.
The drive modules explained may be used in particular for driving luminous means in motor vehicles. In this case, customary luminous means are incandescent filament lamps or arrangements having one or a plurality of light emitting diodes. Light emitting diode arrangements of this type are referred to hereinafter as LEDs for short. In order not to have to provide a plurality of different modules for driving different luminous means, it is desirable to be able to use one drive module optionally for driving an incandescent filament lamp or for driving LEDs. This has been problematic hereto since a drive module optimized for driving an incandescent filament lamp does not function, or functions only inadequately, for driving a light emitting diode, as is explained below.
In order to improve the EMC compatibility, drive modules for incandescent filament lamps are dimensioned such that the rising and falling edges of a voltage present across the load which arise during the switching operations do not have an excessively steep or somewhat flattened profile. Such an edge profile may be unsuitable, however, for driving LEDs. LEDs are driven in pulse-width-modulated fashion for setting the brightness of the light that they emit. If very small duty ratios (duty cycles) are chosen for the pulse-width modulated driving, with the consequence that the pulse durations of the voltage pulses that drive the load become very short, it can happen in the case of shallow voltage edges that the voltage pulses do not reach their maximum value. A reliable diagnosis in the module, such as, for example, a reliable determination of the load current flowing is not possible in this case, however.
For these and other reasons, there is a need for the present invention.